Masao Shimoji

Analysis of a conical optical beam deflector insensitive to motor wobble

The analysis of a patented optical beam deflector based on a rotating prism is presented. It is shown that because of the transmissive, as opposed to reflective, nature of the proposed deflector, the resulting scan spot is for all practical purposes completely free of the tracking error that is so problematic to all reflective-type deflectors. In addition, if a conical scan is either acceptable or desirable, the scan lens design will be much simpler because the f - θ condition is not required and the scan field is inherently flat.

Prospects for Optical Interconnects in Distributed, Shared-Memory Organized MIMD Architectures

The antipodes of the class of sequential computers, executing tasks with a single CPU, are the parallel computers containing large numbers of computing nodes. In the shared-memory category, each node has direct access through a switching network to a memory bank, that can be composed of a single but large or multiple but medium sized memory configurations. Opposite to the first category are the distributed memory systems, where each node is given direct access to its own local memory section. Running a program in especially the latter category requires a mechanism that gives access to multiple address spaces, that is, one for each local memory. Transfer of data can only be done from one address space to another. Along with the two categories are the physically distributed, shared-memory systems, that allow the nodes to explore a single globally shared address space. All categories, the performances of which are subject to the way the computing nodes are linked, need either a direct or a switched interconnection network for inter-node communication purposes. Linking nodes and not taking into account the prerequisite of scalability in case of exploiting large numbers of them is not realistic, especially when the applied connection scheme must provide for fast and flexible communications at a reasonable cost. Different network topologies, varying from a single shared bus to a more complex elaboration of a fully connected scheme, and with them the corresponding intricate switching protocols have been extensively explored. A different vision is introduced concerning future prospects of an optically coupled distributed, shared-memory organized multiple-instruction, multiple-data system. In each cluster, an electrical crossbar looks after the interconnections between the nodes, the various memory modules and external I/O channels. The clusters itself are optically coupled through a free space oriented data distributing system. Analogies found in the design of the Convex SPP1000 substantiate the closeness to reality of such an architecture. Subsequently to the preceding introduction also an idealized picture of the fundamental properties of an optically based, fully connected, distributed, (virtual) shared-memory architecture is outlined.

Free-space optoelectronic data distributor for fully connected massively parallel processors

A Code V simulation of a free-space optoelectronic data distributor, commonly known as the Kaleidoscope, is presented. The device is designed to interconnect processing elements in massively parallel processors, and the simulation results indicate that the device is capable of interconnecting 64 processing elements with a 64-bit word in a fully connected topology. The results further suggest that the number of processing elements, in the future improved version of the device, may be increased to 1024 and beyond.

Confocal scanning optical microscope with circular scan line

A reflected-light confocal scanning optical microscope with circular scan line is described. For the horizontal scanning, the instrument uses a rotating dispersive prism embedded at the tip of a hollow motor shaft. The rotating hollow motor shaft accepts a polarized collimated laser beam and transforms it into a rotating beam, with a cone-shaped trajectory, on its exit from the prism. The rotating beam then passes through an inverted telescope and a quarter-wave plate before it is focused onto the specimen plane by a conventional microscope objective. To improve upon the ranging accuracy, a telecentric scan is maintained throughout the scan. The reflected light travels back through the same components until it is redirected by a beam splitter to pass through an analyzer and a pinhole before arriving at the detector. The use of the same optics for both illumination and imaging automatically satisfies the confocal requirement, and eliminates the need for a synchronizing mechanism. Also, the use of a rotating prism renders the system completely insensitive (for all practical purposes) to motor wobble.

Inherent image distortions of an optical fan-out device, the Kaleidoscope

An optical imaging device coined by its originator, E.E.E. Frietman of The Delft University of Technology, as the Kaleidoscope was first proposed in the early eighties as an optical backbone for interconnecting processing elements in a large parallel computer. The Kaleidoscope consists of three components of an imaging lens, faceted mirror, and optical fiber arrays, and possesses considerable data fan-out potential. In this paper we present simulation results, in the Gaussian domain, that reveal image distortions inherent in the Kaleidoscope.

Afocal attachment to a conical optical beam deflector insensitive to mechanical motor wobble

An afocal optical system designed to be attached to a conical optical beam deflector is discussed. The conical beam deflector generates a collimated optical beam that rotates along a cone-shaped trajectory in space. This output beam is then fed to the afocal attachment, a telescope, designed to tailor the beam characteristics to suit a particular application. For many applications, the afocal attachment functions as a beam expander and modifies three characteristics of the input beam. First, it expands the input beam diameter to an acceptable level. Then, it inevitably reduces the apex cone angle of the beam due to the inherent property of a telescope. Third, the stationary plane, the plane where the apex of the cone resides, is magnified and transferred to the conjugate image plane.

A closer examination of Fresnel and Fraunhofer regions in the scalar wave diffraction theory

The regions of validity for both the Fresnel and the Fraunhofer diffraction regions are examined. The neglected phase terms in the general formalism of scalar diffraction theory are attributed to the secondary Huygenss sources over the aperture and a geometrical argument leads to an equation of a curve defining the Fresnel region. It is found that the boundary profile of the cone-like Fresnel region is a slowly varying function of three-fourths the power of z, the direction of wave propagation. Both the Fresnel and the Fraunhofer regions are deduced from a simple phase error criterion and we find them to be the solids of rotation bounded by the z to the three-fourths power curve.<<ETX>>

Principle of operation of a refractive optical beam deflector and its properties as a photonic switch

An optomechanical photonic switch that exploits the stationary property of the minimum deviation angle of a dispersive prism is described. The switch is based on an optical beam deflector consisting of an electric motor with hollow shaft. The tip of the motor is fitted with a dispersive prism and the deflected beam is focused onto pixels arranged around a circular scan track. It is shown that the proposed switch is, for all practical purposes, completely insensitive to mechanical wobble of the motor. Furthermore, the existing technology suggests that such a small-inertia motor with no external load may achieve speeds up to hundreds of thousands of revolutions per minute and beyond. We suggest one application of the switch as a write gate of a time slot interchanger in the time-division switching of pulse code modulation (PCM) codes. It is shown that the proposed switch can achieve speeds up to and exceeding hundreds of megabits per second.

Study of eigenmode propagation and simulation of multiconductor microstrip transmission line crosstalk

The time response of coupled microstrip transmission line, obtained by modal analysis in frequency domain, has been studied. The authors have examined both voltage and current waves at each frequency component of the source by writing them explicitly in terms of eigenmodes. It is seen that, in general, all eigenmodes, whose numbers are equal to the number of signal conductors, are present in both voltage and current waves. Each eigenmode in turn contains forward and backward traveling components whose amplitudes are determined by terminal conditions. It is also pointed out that eigenmodes travel at slightly different velocities from each other. However, if the line is lossless the velocities for each eigenmodes are independent of frequency.<<ETX>>